My 99 Ranger had a #5 cylinder misfire error code so suspecting a plug problem I switched plugs between #5 and #4 cylinders and after driving about 40 miles had the error code read again which came up #4 cylinder misfire. I replaced the double platinum plug in cylinder #4 which cured the engine problem; but now I have a problem with Autolite....they won't honor the 5 year or 100,000 mile guarantee claiming I damaged the plug at installation.
That doesn't fly as I had about 30.000 miles on that plug before a problem started which grew from an occasional misfire to rather steady power loss from misfireing ; especially uphill.
I have been advised by the local parts store to buy Motorcraft from now on as they are still made in the U.S.; so the parts store is suggesting the Autolite made in Mexico is substandard quality. I still have the full set of Autolites in the engine which is running fine; but at the first sign of trouble they are getting yanked!

Check the insulator. It is a common thing to fracture or crack during installation by trying to apply to much torque or have the socket offset due to trying to reach the plug hole. I had one act the same way after 13,000 miles. It was a hairline crack in the insulator. It was on one of the cylinders that was a b*t*h to reach.

Concerning the spark plug failure rejection of guarantee....I have been doing my own plug changing for forty plus years and have worked in a prototype machine, welding and assembly shop for 25 years moving up to drafting and engineering assistant writing specs and making design changes. I have never cracked the porcelain on a spark plug during installation or disassembly through a dozen different vehicles over the years. I will tell you the plug in question had lines in the porcelain that could have been cracks but could also have been electrical discharge discoloration (which I suspect is the case) from internal breakdown of intended electrical function. Granted there are many possibilities for why the plug failed; but fail it did; even though the five other plugs I installed at the same time continue to function properly; and the company is attempting to shift the blame by circumventing the guarantee. For that reason I will never buy Autolite again and will encourage everyone I know to steer clear of Autolite.
No company can boast 100% quality control. That is why guarantees were created. All I want is the free plug replacing the defective one but Autolite just wants to cover their lying butt by making the consumer look like a jerk who doesn't know a spark plug from a tail pipe. They picked the wrong boy to thumb their noses at! Their type of company profile must be eliminated by consumer savvy of those companies who value customer input and loyalty.

This is an update to the Autolite plug misfire. While initially the one plug replacement corrected the problem; a few days later the engine was sputtering again; although not nearly as bad as before; but as I previously promised if anything went wrong again; I pulled ALL six plugs including the new Autolite I just bought and replaced them with Motorcraft plugs as some of you suggested; and in addition i replaced the AUTOLITE plug wires as well with Durolast which have a limited lifetime guarantee offered by Auto Zone ( but not the plugs).
Upon examination i did note tiny amounts of corrosion on the wire terminals that plug into the distributor block; and I guess there is probably more corrosion inside the wires causing the erratic engine behavior because after these replacements the engine is purring like it should once again!
Thanks again to all who contributed info here! Much appreciated!
Wilson

And one additional note about the Autolite plugs....I checked Walmart and that's what they are selling at a red tag discount which tells me my problem is well recognized by the manufacturer who Walmart admits by their discount is substandard....which tells every serious vehicle maintenance person to steer clear of Autolite!

I've been driving my ranger from new for 10 years and have more than 125,000 miles on it. I can tell you to keep an eye on the thermostat....mine failed before I noticed the heat gage pegged and cracked the heads which had to be replaced by my local garage who did it wrong and now my front right cylinder burns oil excessively. When I complained to them they said they wouldn't do anything to fix it and that's the last time I went to them. So I've been adding Rislone every week and keep the oil level close to full but I'm burning a quart about every 500 miles. Fortunately it isn't enough to compromise the oxygen sensors or the catalytic converter so I am living with the poor replacement job. Other than that I have been happy with the Ranger's performance and hope you have the same good experience with your new Ranger!

I believe alot of additives are just hype. But I had an old 72 Ford F-250 with the 360 in it. I lived 11 miles from work. It burned 1 quart of oil each way! I put in a can of engine restore & it only burned a quart every 600 miles. Quite the improvement yes?

It's been awhile since I tried a different additive to slow oil consumption. I have lost track of how many different additives I have tried; including "Restore". I have pulled that front right cylinder plug several times to observe how it is fairing under the high oil condition and it always has white residue which seems odd so I am thinking there may well be a coolant leak into the cylinder as well suggesting the gasket has a small tear or piece of grit preventing it from sealing properly. I really shold pull the head off to find out the specifics as it could be something simple but then again if it is a head crack from improper assembly a lot more work will be entailed than I may have the expertise to perform.
I have set valve clearances in the past on a different vehicle but that is as deep as I have gone into an engine.
Perhaps I will try another can of the "restore". It couldn't hurt! Thanks!